Steering operated control mechanism for electric motor drives of vehicles



1 c. F. BALL EI'AL 2,571,180

STEERING OPERATED CONTROL MECHANISM FOR ELECTRIC MOTOR DRIVES 0F VEHICLES Filed Aug. 16, 1946 3 Sheets-Sheet 1 6 b o o o 0 ni' 'm i 6/202265 F BaZ James 217. Z1100 Oct. 16, 1951 B ET AL 2,571,180

C. STEERING OPERATED CONTROL MECHANISM FOR ELECTRIC MOTOR DRIVES OF VEHICLES Filed Aug. 16, 1946 3 Sheets-Sheet 2 gl'llm 9 'Z /6 g I 0%? 09 S 530622202 5; I I9 67202265 133022. \A\\ g 272/ /0 Z 5 Oct. 16, 1951 Q BALL ET AL 2,571,180

STEERING OPERATED CONTROL MECHANISM FOR ELECTRIC MOTOR DRIVES OF VEHICLES 5 Sheets-Sheet 3 Filed Aug. 16, 1946 122210225026: [220226517 3622. James M ZflooZ/Z 33/ Amifl'm ptou Patented Oct. 16, 1951 STEERING OPERATED. CONTROL MECHA- NISM FOR' ELECTRIC MOTOR DRIVES OF VEHICLE S Charles, E. Ball and- James. W. Woolf, Franklin, Pa... assignors; to Joy Manufacturing Company, a corporation of Pennsylvania Application August 1 6, 1946, Serial No.- 690,856

6 Claims.

go almost any placein a mine where passageways. are available, and that'they be able to travel. at.

different speeds under different conditions, and

that-they'be able to maneuver about corners. and

elsewhere on very short radii. Because of the nature of their use, it has-been found thatitis very desirable to use; series motors, one'for each of'a pair of wheelsat oneend of the vehicle, and

to be able to operate such motors either in series with each other or in parallel. Such an arrangement is peculiar-lyadapted to use with a vehicle having its normally rear wheels each separately motor driven, and utilizing a centrally disposed steering wheel arrangement at its normally forward end. Such an arrangement through the special nature of the loadsimposedbythesteer ing, especially on very-sharp turns, makes possible in effect an electrical differential actionof a peculiarly desirable nature.

It will be understood that each separately motor driven driving wheel sets up forces which tend to shifttomove bodilythe steering wheel towards the opposite side of the straight path along which the machine travels when the steering device is centrally adjusted. When the steering wheel or-wheels are rotating on an axis oron axes ina plane to which the axial line of the vehicle is perpendicular, these forces balance each other outin practice. Then each motor nicely counterbalances the action of the other, and-the vehicle moves forwardly smoothly and easily in a straight line. When the steering wheel or wheelsare angled towardsone side or-the. other, the driving wheel at the side towards which they are angled is placed under an increased load'and tendst move the steeringwheel or wheels transversely totheir planes of rotation, and whenthe steering adjustment is such asto secure very sharp turning, the load onthemotor'on the inside of the turn ismuch increased while the;

load onthe other; motor is not correspondingly afiec-tedby the wheel-angle. By choosing motorp Sufiicient or ransportat on. needs: butpreferably. below that which. would tend toproe duce undesired skidding ofthe steering wheel; tires, by providing for the changefrom parallel. operationof the. motors which drive the wheels t operation in series when sharp turns are to be negotiated, and, if desired, though this i not. essential with respect to the broader aspects of our invention, providing means for effecting an automatic change from parallel to series-connec tion when the horizontal angle of the steering: wheels to the axial li-ne ofthebody-of the vehicle exceeds a predetermined selected number of de-' grees, a very efficient arrangement can be pro-- duced; and is produced, by ourinvention.

An object. of: ourinvention is to provide an improved, highly maneuverable electrically driven Another object of our inention is to:

vehicle. provide an improved motorcontrol system. Still another object ofourinvention is to providean" improved series-motor drivenvehicle, having improved means for effecting the operation of its mutually independent driving'motors inseries or in parallel, and having particularlycooperation between the motors and a centrally arranged steering mechanismsothat an electrical differential is-in effect-produced. Still a furtherobject of our invention is to provide an improved electrical controlling means forthe driving motors of a readily steerable vehicle. Other objectsandadvantages ofour invention will appear in the course-or the following specification and the appended claims.

In the accompanying drawings, in which'oneillustrative.- embodiment of. our invention in-its.

broader aspects, and including a refinement which is desirable, but not essential to the broader aspects of our invention, is'shown for purp'osesof illustration.

Fig. 1 is a top plan view of'a vehicle-herein shownxin the form of "a utilitymining truck in which the illustrative embodiment of ourinvention is. embodied.

Fig. 2: is a side elevation of the vehicle shown inFig. 1.

Fig. 3-. is. a transverse, vertical section onthe planeofthedine 3L..-.3:of Fig. 1, illustrating steering devices.

Fig. 4 is a fragmentary, longitudinal, vertical sectionon thaplaneof the. line 4-4" of Fig. 1- showing an illustrative wheel driving unit.

Fig. 5 isa vertical, transverse section on theplane of the line.5-5 of Fig. 4.

Fig. 6 is a diagrammatic-drawing-of thecircuits and control devices ofv the vehicle illustrated in the other figures.

And Fig, 7. is a fragmentary diagrammatic-secs :of the apparatus.

tional view showing one arrangement for securing steering angle control of motor hook-up.

Referring now to the drawings, and initially to the first two sheets thereof, it will be observed that we have shown a vehicle I having at the opposite sides of its rear end propelling or traction wheels 2 and 3. Each of these wheels has its own driving motor 4, these motors being desigthe hub l2 of a rubber tired wheel I3 is keyed at 4 I4. The several rotating parts mentioned are suitably journaled in a multipart casing 15 supported as at IS, IT, with the motor 4, on a side wall of the body l8 and on a flange or shelf l9 secured to said side wall in any suitable manner. Each of the motors 4 is a series motor, D. C., and designed to be battery driven in the normal use Brakes, not shown, may be provided for the wheels. Each is of a power suited to the needs of the apparatus, and of a speed suited to provide the desired operating speed with reduction gearing as described. The motors are intended to be driven in series or in parallel,

as later described.

For the steering of the apparatus there is mounted in a suitably shaped casing 2|] formed at the forward end of the vehicle, by means of any suitable bearing arrangement 2|, a vertically extending tubular shaft 22, having a collar 23 secured to its lowerend, and this collar carries a pair of oppositely disposed stub axles 24, 24, for receiving pneumatic tired wheels 25. The axles 24, 24 slope downwardly from the collar 23, so that the bottom or ground-contacting surfaces of the wheels 25 are close together, and in effect may be considered as providing a single wheel of dual construction for supporting the front end of the vehicle.

The tubular shaft 22 has a worm wheel 2! secured to its upper end, and a worm carrying a shaft 28, suitably fixed against axial movement and carrying a worm (not shown) engaged with the worm wheel 2'! is adapted to turn the steering wheels and to hold them in difierent adjusted positions. A universal joint connects the worm carrying shaft 28 with a hand wheel controlled shaft 31 which is turned ,by means of a hand wheel 32, the outer end of the shaft 3! being rotatably supported by a suitable bracket 33 secured to the vehicle body.

A drivers compartment 35 is provided at the left forward end of the vehicle, and an operator is able to seat himself on a plate 36 on the bottom of this compartment and support his back against an upwardly bent portion of this plate and operate and control the wheel 32, and also certain other mechanisms which will shortly be described.

The vehicle is provided with battery compartments 3! at its opposite sides, and if either of these be not needed for battery use, obviously it may be used as a utility compartment. The large space between the battery boxes and rearward of the steering mechanism and the operator's or control compartment is provided for the transport of men, tools or materials. A compartment 4| at the side opposite the operators compartment may be used fOr the housing of the controls which will shortly be explained. The vehicle has desirably front and rear headlights, of which only the former, 42, is shown.

Arranged at the forward end of the operators space is a foot lever 44, pivoted between its ends as at 45 and movable by the foot of an operator, providing for the control of a high-low and reset mechanism later described, and there also extends into the right hand side of the operators space a handle 46 controlling through suitable connections not shown a forward and reverse switch mechanism. Finally there projects into the operator space near the rearward end thereof a handle 41 controlling the headlights and a so-called safe-off device. Other, conventional mechanisms not per se afiecting the invention are provided but need not be described in detail.

In the illustrative embodiment of the invention, as will more fully appear as a description of Fig. 6 is given, there are the two wheel driving motors 4A and 4B. Each of these is a series motor with a commutating winding, an armature, and a series field. Each is reversible by forward and reverse contactors. The direction of motor rotation is controlled by the forward and reverse selective switch mechanism controlled by the handle 46. The fast-slow and reset mechanism causes the motors always to be started in series, even when the control lever 45 is pushed through the starting, series-connection effecting position, immediately to the parallel connection position, and also provides for these positions, a reset position, in which it is normally held by a spring 55, a partway-forward position in which it establishes series relation between the two motors, and an all-the-way forward position, in which the two motors are connected to the battery in parallel. The safe off and front and rear light mechanism is a safety switch mechanism which requires operation before the other control devices can be operated to effect any results, and which requires one or the other headlights to be on before the vehicle can be set in motion.

As will be seen, one motor is always operated when either is running. When a series switch, S, later described, is closed, motors 4A and 4B are connected in series across the lines from the battery. One motor will then be very briefly shorted out while the other is connected across the battery, the series switch will then be opened, and then a third switch will be closed and by it the other motor will be connected across the battery in parallel with the first.

Referring now to the diagrammatic view, Fig. 6, it will be noted that the motors are designated 4A and 4B. The battery is shown at Bl. Its positive end is connected by a. conductor 62 with one contact 63 of a main line switch 64. The opposite contact 65 is connected by a conductor 66 to the coil 67 of an overload relay 68. The other end of coil 51 is connected to a conductor 69. A conductor 10 connects conductor 69 with the reversing system of motor 4B, while a, conductor H connects the conductor 69 with one side of a switch Pl, of which the other side is connected to a conductor 12 from which branches 13 and 14 lead respectively to the reversing system of motor 4A and to one side of another switch S of which the other side is connected by a conductor 15 to conductors l6 and 11, the first of which is connected with the series field I8 of motor 4B, while the second leads to another switch, P2, whose opposite side is connected by aconductor 19-and aconductor 80 with the seriesneld'BI of motor 4A, and by a conductor 82 to one side of the other half of the main line switch, and the opposite side of this half of the switch is connected by a, suitably fused connection-'83 with the negative end of the battery.

reversing systems proper of the motor 4A and 4B are the same, and so the system associated with motor 4B only will be described. Conductor is connected by conductors 9I and 92 to switch contacts '93 and 94 respectively. A contact 95, connectible'by a switch element with the contact 93 is conne'cted by a conductor '96 with the commutating winding 91 of motor-4B and through such winding to the armature 98,

through an appropriate brush arrangement. The other brush arrangement is connected by a conductor 99 to conductors I00, leading to a contact 'IOI opposite contact94 and conductor I02, leading to acontact I03, whose associated contact I04is connected by a conductor 1 05 with the series field 18. From the conductor 96 there are branches of conductor I06 leading to a contact I01, whose associated contact I08 is connected by a conductor I09 also to the series field 18.

Contact members I I I and H2 moved concurrentl by a solenoid II3 are adapted to connect contact 93 with contact '95 and contact I03 with contact I04, when the solenoid is energized as later explained. Contacts H4, H5, moved concurrently by a solenoid II6, are adapted to conn'ect, when moved to closed positions, the conta'ct 94with the contact IOI and the contact I08 with 'the contact I01. There is an interlock associated with each of the switch devices just described, but not with the corresponding switches associated with motor 4A. These interlocks, which are of the normally open, time delay closing type, are shown for simplicity as actuated by the same armatures that actuate the switch elements III and H2, and the switch elements H4 and H5, but in fact are actuated by the flux of the solenoids, but through delayed action elements of well known commercial design, The

facts that they are not directly actuated by the same armatures and that their actuation is accomplished only 'afer a slight time delay, arcindicated by the letters TD.

"When the contact members III and H2 are closed, the motor 4B is driven in one direction by current passing from 10 through conductor 91, switch 93, I'II,95, conductor 96,commutating winding 91, motor armature 98, conductors 99andI02, switch I03, II2, I04, conductor I05, series field 18, and the conductor 16, etc. When the switches I I4 and [I5 are closed, the motor is driven in the opposite direction by current passing from conductor 10 to conductor 16, as follows: via conductor 92, switch 94, H4, IOI, conductors I00 and 99, motor armature 98, commutating winding 91, conductor I06, switch I01, II5, I08, conductor I09 and the series field 18.

The safe ofi, front'light or rear light device I 20.

may now be considered. This device is controlled by the handle41 and is diagrammatically shown 1 as comprising three contact elements I2I, I22 and I 23 all movable together, and movable in one direction or the other from a central on position. A suitablyfused line I24 leads from the positive line 62 to and is suitably permanently connected to the contact element .I.2I. Contacts I 25 and I26 are selectively engageable by contact element 1 2 I as it is moved in opposite directions. .These are connected together as at I21. Bothare,connectedthrougha conductor I28 with which is connected to the negative side of the battery SI byway of a fuse MI and a portion of the conductor 83. From the foregoing descrip-' tion it will be clear that either headlight may be 'turned on, dependent on the direction of movement of the device I20, and it will further be noted that there is a branch I42 of the line I29 which connects with one side of an interlock switch mechanism associated with the main line switch M and which is closed when the main line switch closes, and which when closed establishes a holding circuit for the main line switch through a conductor I44 leading to the negative conductor I40. Moreover, when interlock switch I43 is closed, current is supplied to the fastslow-reset mechanism as later noted, but attentionlmay now be called in passing to the conductor I58.

When handle 41 (shown in Fig. 2) is moved manually to the front light or rear light (depending on the contemplated direction of motion) operating position, line I29 is connected to'the positive terminal of the battery 6| as follows: conductor 62, conductor I24, contact I2I, contact I25 or I26 depending on the initial setting, conductor I28 (by way of conductor I21 if contact I26 is engaged), and the normally closed contacts of overload relay 68.

The fast-slow-reset mechanism is generally designatedI50, as noted above, and it is operable by the foot lever 44 and includes a reset arrangement, an arrangement for effecting connection of the'motors in series, and an arrangement for effecting their connection in parallel. These are diagrammatically illustrated at I 5I, I5IA, and I5IB. While any suitable arrangement may be used in practice, the device I5I is shown as comprising a contact I52 to which positive line I29 leads, a contact I 53 connected to a contact element I51 by a conductor I54, and a movable cont-act I55 which connects the contacts I52 and I53 when the three devices I5I, I5IA and 'I5IB are in reset position. The contact I51 of the device IE0 is connected by a conductor I58 to the lower end of the main line switch solenoid I59, at a point nearer the latter than the interlock'l43. Contact I51 is adapted to engage a stationary contact I60 and when so engaged to effect closure of switch S and connection'ofv the. motors 4B and 4A in series to the battery 6I. Movable contact I6I of device I5IB is adapted to cooperate with a stationary contact I 62 when the foot lever is in full forward position and to thereby effect, as later described, connection of the motors in parallel to the battery. The contacts I55, I51 and I6I are movable together, but not, aside from the connection I54, electrically connected With each other.

Before describing further the functions of the mechanism I50, forward-oif-reverse mechanism I10 may well be described. This includes three contact elements I1'I, I12 and I13, all electrically connected, and all movable together, and having a neutral position as shown, and selectively oppositely movable by the handle 46 to effect selective forward or reverse drive. Contact I1I connects with one or the other of connected contacts I and I15 in one of the turned positions of the device I10. It is connected by a conductor I18 with the contact I60. When device I10 is moved in one direction, contact I12 contacts a stationary contact I80, and when device I10 is turned in the opposite direction, the contact I13 connects with a contact I8 I.

Contact I8I is connected by a conductor I82 having branches I83 and I84 to the solenoids H6 and H6 and these solenoids are connected by conductors I35 and I85 to the line I40. Hence when contact I13 is in engagement with contact I8I when current is delivered to I60, the motors will turn in one direction. Contact I80 is connected by a conductor I81 and branch conductors I88 and I89 to the solenoids H3 and H3, and the other ends of these solenoids are connected respectively by conductors I90 and I9I to the line I40. Thus when contact I12 and contact I80 are in contact and current is being delivered to contact I60, the motors will both turn in the other direction.

It has been noted that time delay action devices, which may now be noted to be numbered I and 202, are associated with the reverse switch mechanisms of motor 43, and that in whichever direction this motor is connected to run one of these devices 20I or 252 will be closed.

Their closure provides, when current is being supplied to contact I60, for current to be supplied to contact IBI a second or so after the running connections for the motors are established. This, for example, because current from I63 (when contacted by I51) will flow via conductor I18, contact I1I, say contact I12, contact I83, conductors I31 and I88, the conductor 283, switch device 20I, conductor 235 and conductor 206 to contact element I6 I, and thence may flow to line 203 when contact I6I engages contact I62. Line 208 contains, as shown, a pair of normally closed switches 209, 2I0, which may be opened by cams turned by the tubular shaft 22 or by the worm shaft 21, on an extended portion thereof within the casing, these cams opening the switches which they respectively engage only when the steering wheels are turned hard over, so to speaknot necessarily to extreme position, but at an angle at which it is desirable to reduce the power exerted by the motor towards whose side of the vehicle the steering wheels have been turned. The arrangement actually illustrated involves cams CI and C2 on the hub of the worm wheel 21. These cams and the switches may be omitted, and the conductor 208 directly connected with the conductor 2I I if desired, so far as the broader aspects of the invention are concerned. Switches 209, 2I0 may, for example, be of the hatchway type. Beyond the switches 209, 2 I 0 the extension of line 208 is numbered 2I I, and it connects, by a branch 2 I2, to a normally closed switch 2I3 movable with and opened by s'witchS when the latter is closed, the other side of switch 2I3 being connected by a conductor 2I4 to the operating coil 2I5 of switch P2, whose opposite end is connected by a conductor 2I6 to the line I40. Another branch 2I1 of line '2II goes to the operating coil 2I8 of the switch PI, and the other side of this coil 2I8 is connected by a conductor 2 I 9 back to the line I40. Switch PI has a switch 22I movable with it, normally closed, but opened when switch P2 is closed, and controlling current flow to the operating coil 8 222 of the switch S. When contact I1I engages. either I15 or I16 and current is being conducted to contact Ill, current will flow by way of 0011-, ductor 223 to switch 22I, through the same when closed, through a conductor 224 to the operating coil or solenoid 222, closing switch S, and then to conductor I40 by way of a conductor 225. When switch PI closes, switch S will be noted to open.

The further mode of operation may now be. noted. When the device I50 is turned or moved to the right in Fig. 6, contacts I52 and I53 will be left by contact I55, and if the solenoid I59 is for any reason deenergized, as by an overloads taking place, resetting by return of contact I50 to the position shown will be necessary to re.- closure of the main line switch.

Now, assuming that the device I10 has bee set to predetermine the direction of motor operation, movement to the right of switch element I51 into contact with contact I60 will bring about closure of the selected direction controlling switches and closure of switch S, and the motors, will be connected in series across the battery in a manner that will be obvious from what has been said, the current passing through motor 43, through conductors 16, 15, switch S, conductors 14, 13, and motor 4A in series. When device I50 is turned further to the right and switch element IBI establishes contact with contact I62, the line 208 will be energized; and assuming that the switches 200 and 2I0 are closed, the solenoid 2 I8 of switch PI will be energized and that switch will be closed, shorting out motor 4B very briefly, and then, because closure of switch PI opens the circuit through the solenoid 222 of switch S, the latter will open, terminating the short circuiting of motor 4B; and, as switch S opens, it will, through the movement of switch 2I3, close a circuit through which the solenoid 2I5 of switch P2 will be energized, and motor 4B will be placed in parallel with motor 4A across the battery, motor 4A having been connected across the battery when switch PI closed.

The mode of operation of the control mechanism will be clear from what has been said, and it appears unnecessary to repeat the details of circuits established during the operations mentioned. It may be observed, however, that because the current to conductor 20B is controlled by one or the other of switches 20 I, 202, the motor direction control effecting actions must be completed before the devices operated off conductor 208 can be energized.

Desirably a mechanical interlock may be pro-- vided between switches P2 and S absolutely to insure against both being closed at the same time with PI also closed through sticking of the parts or any mechanical difficulty. Such an interlock (not shown) may be in the form of a pivoted lever connected with the movable switch parts of switches S and P2 so that each may be closed separately, but not both together.

The various controls, especially the mechanisms I20, I50 and I10, and switch devices 20I and 202, are shown very much in diagrammatic form, for simplicity of illustration, and it will of course be understood that arrangements for making movable parts stationary and vice versa are all within the scope of our invention.

Now, with respect to the series-parallel operation of the motors, it will be evident that during straight line movement or movement on curves of large radius, there will be no difficulty even though one motor may develop more torque, ata.'slower speed on the curves just mentionedL- This. will, indeed, provide a differential-like action with the outside traction wheels turning faster. When, however, it is desirable to turn sharply-to cramp the wheels well around-it will be desirable to slow the vehicle down, a thing which releasing the pedal halfway and going to series motor operation will accomplish, and it will also be desirable to reduce the torque exerted by the motor on the inside of the sharp turn, and to have the advantage of the relative speeding up a greater relative speeding upwhich will follow the taking by the motor on the outside of the sharp curve of more than half of the voltage. Accordingly, in series operation, it will be seen that not only will an increased differential action be produced but also the reduction in the torque exerted by the "inside motor will reduce the chance of tire slippage which would otherwise be much increased by reason of the fact that at the extreme angle the tires would make, with respect to the inside motor, that motor could exert little steering wheel rctative effect,

From what has been said, it will be appreciated that this invention provides a very useful and desirably functioning vehicle, having adaptability to other uses, but operative very effectively in mines. The controls, especially without the switches 209, 210 and their operating mechanisms, if these be omitted-and these are to be understood as refinements, ratherthan essential features of the broad phases of the invention, and might be omitted without detriment to the invention in its broad aspectsare very simple, effective, guard against harmful results of oversight, and it may be noted that even were the operator to push the pedal forwardly all the way without any delay, the motors would still be started in series, though they would in a few seconds or so pass through the series connection stage and be in parallel across the battery.

The dual motor circuit disclosed but not claimed herein is the subject matter of a divisional patent application Serial No. 790,425, filed December 8, 1947, now Patent 2,530,278Woo1f, issued November 14, 1950.

While there is in this application specifically described one form which the invention may assume in practice, it will be understood that this form of the same is shown for purposes of illustration, and that the invention may be modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent is:

1. In a vehicle, a body having front and rear ends and two sides and running gear including opposed drive wheels at the sides for one end and a steering wheel arrangement for the other end, a source of current, separate series driving motors for driving said drive wheels, means for selectively connecting said motors in series with each other to said source of current or in parallel to said source of current, said connecting means including a circuit comprising a pair of coils in parallel and connected to close parallel circuits for said motors when energized and normally closed switches in series with said pair of coils, the connecting means further including circuit means to control connecting the motors in series and means governed by one of the aforesaid pair of coils to interrupt the series connection of the motors, and means governed by the angle of the steering wheel arrangement for opening said normally closed switches whereby the circuit of the pair of coils is interrupted and the aforesaid means governed by one of the aforesaid pair of coils operates to connect the motors in series.

2. In a vehicle, a body having front and rear ends and two sides and running gear including opposed drive wheels at the sides for one end and a steering wheel arrangement for the other end, a source of current, separate series driving motors for driving said drive wheels, means for selectively connecting said motors in series with each other to said source of current or in parallel to said source of current, said connecting means including a circuit comprising a pair of coils in parallel and connected to close parallel circuits for said motors when energized and normally closed switches in series with said pair of coils, the connecting means further including another circuit comprising a coil to control connecting said motors in series and a normally closed switch in series with said series control coil and connected to be opened by energizing one of the aforesaid pair of coils, and means operative when the steering wheel arrangement attains a predetermined angle to said body for opening the aforesaid normally closed switches.

3. In a vehicle, a body having front and rear ends and two sides and running gear including opposed drive wheels at the sides for one end and a steering wheel arrangement for the other end, a source of current, separate series driving motors for driving said drive wheels, means for selectively connecting said motors in series with each other to said source of current or in parallel to said source of current, said connecting means including a circuit comprising a pair of coils in parallel and connected to close parallel circuits for said motors when energized and a pair of normally closed switches in series with each other and in series with said pair of coils, the connecting means further including circuit means to control connecting the motors in series and means governed by one of the aforesaid pair of coils to interrupt the series connection of the motors, and means operative when the steering wheel arrangement attains a predetermined angle to said body for shifting the connection of said motors with said current source from parallel to series, if they are at that instant connected in parallel to said source, said shifting means including a pair of cams actuable by the steering wheel arrangement upon movement of said arrangement into said predetermined positions, the cams being actuable as aforesaid to open said pair of switches.

4. In a vehicle, a body having front and rear ends and two sides, side rear wheels, a front, centrally disposed steering wheel arrangement, separate series driving motors for driving said rear wheels, means for changing the connections of said motors to effect their rotation in either di rection, a source of electric current, means operating through the aforesaid connection changing means for selectively connecting said motors in series with each other to said source of current or in parallel to said source of current, said connecting means including a circuit comprising a pair of coils in parallel and connected to close parallel circuits for said motors when energized and normally closed switches in series with said pair of coils, the connecting means further including circuit means to control connecting the motors in series and means governed by one of the aforesaid pair of coils to interrupt the series connection of the motors, and means governed by the angle of the steering wheel arrangement for opening the aforesaid normally closed switches whereby the circuit of the pair of coils is interrupted and the aforesaid means governed by one of the aforesaid pair of coils operates to connect the motors in series.

5. In a vehicle. a body having front and rear ends and two sides, side rear wheels, a front, centrally disposed steering wheel arrangement, separate series driving motors for driving said rear wheels, means for changing the connections of said motors to eifect their rotation in either direction, a source of electric current, means operating through the aforesaid connection changing means for selectively connecting said motors in series with each other to said source of current or in parallel to' said source of current, said selectively connecting means including a circuit comprising a pair of coils in parallel and con- :nected to close parallel circuits for said motors when energized and normally closed switches in 'serieswith said pair of coils, the connecting means further including another circuit comprising a coil to control connecting said motors in series and a normally closed switch in series with said series control coil and connected to be opened by energizing one of the aforesaid pair of coils, and means operative when the steering wheel arrangement attains a predetermined angle to said body for opening the aforesaid normally closed switches.

6. In a vehicle, a body having front and rear ends and two sides, side rear wheels, a front, centrally disposed steering wheel arrangement, separate series driving motors for driving said rear wheels, means for changing the connections of said motors to effect their rotation in either direction, a source of electric current, means operating through the aforesaid connection changing means for selectively connecting said motors in series with each other to said source of current or in parallel to said source of current, said selectively connecting means including a circuit comprising a pair of coils in parallel and connected to close parallel circuits for said motors when energized and a pair of normally closed switches in series with each other and in series with said pair of coils, the connecting means further including circuit means to control connecting the motors in series and means governed by one of the aforesaid pair of coils to interrupt the series connection of the motors, and means operative when the steering wheel arrangement attains a predetermined angle to said body for shifting the connection of said motors with said current source from parallel to series, if they are at that instant connected in parallel to said source, said shifting means including a pair of cams actuable by the steering wheel arrangement upon movement of said arrangement into said predetermined positions, the cams being actuable as aforesaid to open said pair of switches.

CHARLES F. BALL. JAMES W. WOOLF.

REFERENCES CITED The following references are of recordin the file of this patent:

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